For sputtering with a target, there is known a method of film formation with a metal compound which comprises introducing a reactive gas followed by reacting the reactive gas with a metal (reactive sputtering method). This method is characterized in that, in general, Al, Si or the like is used as the target, a rare gas such as He or Ar is used as the process gas, and O2, N2 or the like is used as the reactive gas; and that the target is reacted with the reactive gas and, as a result, a metal compound is formed on a substrate.
For high-speed film formation according to conventional reactive sputtering, employed is a method of controlling the reactive gas flow rate by monitoring the plasma emission intensity, the voltage and the inner pressure followed by feeding the data back to the mass flow controller (see U.S. Pat. No. 4,166,784). In this method, however, in case where the film formation speed greatly differs between metal and metal compound such as Al and Al2O3 and when a metal compound having a sufficient stoichiometric ratio is formed into a film through reactive sputtering, then there may occur a problem in that the film formation speed of the metal compound is relatively low as compared with the film formation speed of the metal alone.
As another method, there is known a substrate bias method which comprises applying a bias to a substrate to promote the reaction of a reactive gas and a metal on the substrate when a film of a metal compound is formed on a substrate (e.g., JP-A 4-154963). In this method, the film formation speed is high since the film formation is carried for a metal; in this, however, the film formed is re-etched on the substrate, therefore causing a problem in that the film surface may be roughened and the film density may lower.
In addition, also known is a modification of the substrate bias method, in which magnets are provided on the back of the substrate to lower the discharge voltage thereby to prevent the formed film from being re-etched, and the modified method satisfies both the film damage reduction and the high-speed film formation (JP-A 58-133376). However, in the method described in JP-A 58-133376, magnets are so provided to the carousel-type substrate holder that they may generate a magnetic field in the direction parallel to the rotary axis direction of the carousel, and therefore, electrons rotate on the periphery of the carousel. Accordingly, in this, when the electrons are not discharged on the entire periphery, the electrons may be shifted and the efficiency may worsen. Therefore, in the method, the discharging must occur in every site on the carousel periphery, and continuous film formation that requires substrate change is impossible.
One reason for lowering most the production speed in film production in a mode of vacuum film formation is that vacuum breaking and degassing into vacuum takes too much time. To solve the problem and to improve the producibility, continuous film formation such as roll-to-roll film formation not requiring vacuum breaking is desired, and a sputtering apparatus is desired, which may be driven at a high film formation speed and may secure continuous film formation with less damage to the formed film.
A conventional reactive sputtering apparatus is described with reference to FIG. 4. In FIG. 4, 1 is the traveling direction of a supporting substrate, 2 is the supporting substrate, 3 is a rotary pump, 4 is a turbomolecular pump, 5 is a vent, 6 is an earth shield, 7 is a pass roll, 10 is cooling water, 11 is a drum, 12 is a chamber, 13 is an RF power source for matching box and drum, 15 is a vent, 17 is a target, 19 is a process gas and reactive gas introduction port, 20 is a magnet for target provided on a cathode, 21 is an RF power source for matching box and target (the same shall apply also to FIGS. 1, 5 and 6).
In the reactive sputtering apparatus, a continuous film is used as the supporting substrate, and the continuous film is conveyed with the drum. From the RF power source 13 for matching box and drum, a power is applied to the supporting substrate 2 for film formation thereon, whereby the reactive gas is changed to a plasma state and led on the supporting substrate, therefore promoting the reaction with the metal sputtered from the target 17 to form a thin film of a metal compound on the supporting substrate 2. However, this apparatus could not evade the above-mentioned prior-art problems.